490 



TRANSIT OF VENUS, 1874. NEW ZEALAND. BURNHAM. 



The horizontal intervals of the vertical wires were found on December 21, 

 by means of the transit meridian-mark before described. Ten bisections of 

 the mark were made with each wire (five in each position of the instrument), 

 the horizontal circle being read each time. There being no imperfect hori- 

 zontal transits observed, the intervals are only required in order that the 

 distance of the mean wire from the center wire may be known. 



The following are the circle-readings corrected for runs : 



The wires are numbered as seen from left to right with lamp left. The 

 circle-reading for the mean wire has been taken as 4"'92 greater than for the 

 center wire with lamp left. 



The corrections for runs of micrometers of the horizontal circle were found 

 as below. Each determination is the mean of four or six at different parts 

 of the circle, made usually on the morning after a night's work. 



The vertical circle of the Altazimuth is 15 inches in diameter, read by four 

 micrometer-microscopes, which are attached by binding-thumb-screws to a 

 movable flat ring of bronze, which is screwed at four points to arms projecting 

 from the frame of the instrument ; a form of mounting which, in Captain 

 Tupman's opinion, is not conducive to the steadiness of the microscopes, or to 

 their easy adjustment. 



